The invention relates to a tube consisting of a tube body of a laminate including a metallic barrier layer, a tube head of a synthetic plastics material and a washer of a laminate with metallic barrier layer arranged on the outer surface of the tube head shoulder.
As shown in FIGS. 4 and 5 of U.S. Pat. No. 4,132,331, the margin of the tube body overlaps the washer arranged on the stepped tube head. The washer likewise has a step which is adapted to the form of the tube head shoulder. In this case, the washer functions as a connecting body and has a substantially thicker metal layer than the tube body. This achieves the object that in the proposed inductive welding, the required frequency is adapted to this thicker metal layer so that the metal layer in the tube practically does not heat. The metallic barrier layer in the washer also serves to increase the gas-tightness in the tube head.
Since the washer and the tube overlap between their two metal layers serving as barrier, there lie two synthetic plastics layers which do not possess gas-tightness, so that thus a certain gas permeability is effected.
However, in tubes the important point is that they have an attractive appearance. In order to obtain tube shoulders which are reasonably attractive, the tube head and thus also the washer must be stepped so that the tube can be formed to the head without unsightly doming, such as necessarily develops when one layer is overlapped by another. From this, however, it also follows that the stepped washer must have a thicker metal layer than the tube body, since only then can the draw-moulding operation necessary for production be carried out. This, however, signifies that a substantially dearer laminate must be used, which in itself alone already increases the production costs of tube. Moreover, differences of color toning between tube body and washer material are unavoidable, and since they necessarily lie side by side in the overlap region on the tube shoulder, this is detrimental to the attractive appearance, since two color rings are distinguished on the tube shoulder, possibly yet a third in the region of attenuation of the material of the tube body which must seal the free end of the metal layer.
U.S. Pat. No. 3,260,411 discloses a similar tube where the washer is arranged on the inner surface of the tube head, here rounded, in such a way that the washer engages beneath the marginal region of the tube body on the outer edge of the head, while the outer edge of the washer can be bent back upwards into the head. In this case, a space always remains between the metal layer of the tube body and that of the washer, which space is filled only by synthetic plastics material so that the gas-tightness is impaired in the tube head region.
U.S. Pat. No. 3,700,513 discloses a tube in which the upper margin of the tube body is inserted on the outer surface of the shoulder of the tube head, which necessitates complicated machines and lengthens production; then a tapered shoulder ring is applied and finally everything is welded by pressure and heating, such as by induction.
It is common to all these tubes that very much and more expensive material, which moreover differs from the material of the tube body, is necessary for the washer, on account of its size and configuration, and also on account of the occurrence of waste. In the tube according to the U.S. Pat. No. 3,700,513, moreover, material of the tube bodies is required for insertion in folds on the tube head.
It is an object of this invention to provide a tube of the initially stated kind by which it is possible to save material and to improve the gas-tightness and the appearance in the head region.